RFC 7563

Internet Engineering Task Force (IETF) R. Pazhyannur
Request for Comments: 7563 S. Speicher
Updates: 6757 S. Gundavelli
Category: Standards Track Cisco Systems
ISSN: 2070-1721 J. Korhonen
Broadcom Corporation
J. Kaippallimalil
Huawei
June 2015 Extensions to the Proxy Mobile IPv6 (PMIPv6) Access Network Identifier
Option
Abstract
The Access Network Identifier (ANI) mobility option was introduced in
RFC 6757, "Access Network Identifier (ANI) Option for Proxy Mobile
IPv6". This enables a Mobile Access Gateway (MAG) to convey
identifiers like the network identifier, geolocation, and operator
identifier. This specification extends the Access Network Identifier
mobility option with sub-options to carry the civic location and the
MAG group identifier. This specification also defines an ANI Update-
Timer sub-option that determines when and how often the ANI option
will be updated.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7563.

1. Introduction
"Access Network Identifier (ANI) Option for Proxy Mobile IPv6"
[RFC6757] introduced the ANI mobility option. This enabled a Mobile
Access Gateway (MAG) to provide the Network-Identifier, Geo-Location,
and Operator-Identifier sub-options. When the access network is
WLAN, the Network-Identifier sub-option may contain the Service Set
Identifier (SSID) and the Basic Service Set Identifier (BSSID) of the
Access Point (AP) and the geolocation of the AP, and the Operator-
Identifier may contain the realm of the operator managing the WLAN.
The MAG sends the above information to the Local Mobility Anchor
(LMA). The LMA may use this information to determine access-network-
specific policies (in terms of Quality of Service (QoS), Deep Packet
Inspection (DPI), etc.). Further, the LMA may make this information
available to location-based applications.
While the above mentioned sub-options provide a rich set of
information, in this document we describe the need for extending the
ANI sub-options that are particularly useful in WLAN deployments. In
WLAN deployments (especially indoor AP deployments), it is difficult
to provide geospatial coordinates of APs. At the same time, for many
location-based applications the civic location is sufficient. This
motivates the need for an ANI Civic-Location sub-option. In many
deployments, operators tend to create groups of APs into "AP-Groups".
These groups have a group identifier. The group identifier is used
as a proxy for coarse location (such as the floor of a building or a
small building). The group identifier may also be used to provide a
common policy (e.g., QoS, charging, DPI) for all APs in that group.
This specification provides a sub-option for the MAG to convey a
group identifier to the LMA. The provisioning of the group
identifier is outside the scope of this specification and is
typically done via a configuration mechanism such as CLI (Command-
line Interface) or via Control and Provisioning of Wireless Access
Points (CAPWAP) [RFC5415] [RFC5416].
This document also provides a new sub-option that determines how
often the MAG will update the ANI. In typical deployments, it is
expected that the MAG will update the ANI as soon as it changes.
This is certainly true when the MAG is co-located with the AP. When
a client roams from one AP to another AP, the MAG on the roamed (or
sometimes referred to as the target) AP will provide the new ANI (for
example, the network identifier and geolocation of the new AP).
However, if the MAG is co-located with an Access Controller (also
known as Wireless LAN Controller (WLC)), then a client roaming from
one AP to another AP does not necessarily perform an ANI update. The
WLC handles client mobility between APs and as a result, intra-WLC
mobility is hidden from the LMA.

In such deployments, the information conveyed in the ANI sub-options
(e.g., location) becomes stale and is only refreshed at the time of
lifetime expiry. The MAG could deal with this by sending a Proxy
Binding Update (PBU) whenever a client moves between APs just for the
purpose of updating the ANI sub-option. Alternately, this document
allows the LMA to determine how often it wants to know about the
changes in the ANI sub-option; for example, in some cases the LMA may
not care about the ANI sub-option except at the time of initial
binding, or in some cases it may care about every AP transition. The
sub-option allows the LMA to tell the MAG the desired update
frequency. As always, mobility events or re-registration events will
update the ANI sub-options. The LMA can use the ANI Update-Timer
option to set the maximum frequency at which it wants to receive ANI
updates. This is particularly useful in environments where a MAG
covers a large number of Wi-Fi APs and there is high client mobility
between the APs; for example, in a stadium Wi-Fi deployment, if a LMA
does not want ANI updates any more often than 100 seconds, then it
can propose 100 seconds as the value for ANI Update-Timer.
[RFC6757] provides ANI sub-options to carry geolocation information.
In this document, we provide additional sub-options to carry the
civic location and group identifier. This document also defines an
ANI sub-option to enable a MAG to communicate how often the MAG will
update the ANI information.
2. Conventions and Terminology
2.1. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
2.2. Terminology
All of the mobility-related terms used in this document are to be
interpreted as defined in [RFC5213] and [RFC5844]. In this document,
Civic Location is defined as follows.
Civic Location: There are two common ways to identify the location
of an object, either through geospatial coordinates or by so-
called civic addresses. Geospatial coordinates indicate
longitude, latitude, and altitude, while civic addresses indicate
a street address or sometimes the location within a building (such
as a room number). Civic location refers to the civic address.

3. Protocol Extension
3.1. Civic-Location Sub-Option
The Civic-Location is a mobility sub-option carried in the Access
Network Identifier option defined in [RFC6757]. This sub-option
carries the civic location information of the mobile node as known to
the MAG. The format of this option is defined below.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|ANI Type=4 | ANI Length | Format | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| civic location ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Civic-Location Sub-Option
ANI Type: 4
ANI Length: Total length of this sub-option in octets, excluding the
ANI Type and ANI Length fields.
Format: This specifies the encoding format of the civic location.
The value 0 is defined in this specification as described below.
The remaining values (1 through 255) are reserved.
0: This value denotes Binary Encoding. The location format
is based on the encoding format defined in Section 3.1 of
[RFC4776], whereby the first 3 octets are not put into the
civic location field (i.e., the code for the DHCP option,
the length of the DHCP option, and the 'what' element are
not included). What is included is the two-octet country
code field, followed by one or more civic address elements.
The country-code is a two-letter ISO 3166 country code in
capital ASCII letters, e.g., US. The structure of the civic
address elements that follow the country code field is as
defined in Section 3.3 of [RFC4776].
Reserved: This MUST be set to zero when sending and ignored when
received.
civic location: This field will contain the civic location. The
format (encoding) type is specified in the format field of this
sub-option. Note that the length SHALL NOT exceed 253 bytes.

3.2. MAG-Group-Identifier Sub-Option
The MAG group identifier is a mobility sub-option carried in the
Access Network Identifier option defined in [RFC6757]. The MAG group
identifier identifies the group affiliation of the MAG within that
Proxy Mobile IPv6 domain. The group identifier is not assumed to be
globally unique across different network operators. However, the
group identifier should be unique within an operator network. In
domains spanning multiple operators, it is recommended that the
Operator-Identifier sub-option (defined in [RFC6757]) be used in
addition to the MAG-Group-Identifier sub-option to ensure uniqueness.
When the MAG is configured with a group identifier, the MAG should
send its group identifier in the PBU. Note that the configuration of
this identifier is outside the scope of this specification; the usage
of the identifier by the LMA is left to implementation. The format
of this sub-option is defined below.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|ANI Type=5 | ANI Length | group identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: MAG-Group-Identifier Sub-Option
ANI Type: 5
ANI Length: Total length of this sub-option in octets, excluding the
ANI Type and ANI Length fields. The value is always 2.
group identifier: This is a 3-octet unsigned integer value assigned
to a group of MAGs.
3.3. ANI Update-Timer Sub-Option
The ANI Update-Timer is a mobility sub-option carried in the ANI
option defined in [RFC6757]. Section 4 describes how the MAG and LMA
use this sub-option.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|ANI Type=6 | ANI Length | Update-Timer |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: ANI Update-Timer Sub-Option

ANI Type: 6
ANI Length: Total length of this sub-option in octets, excluding the
ANI Type and ANI Length fields. The value is always 2.
Update-Timer: Update-Timer is a 16-bit unsigned integer. The unit
of time is 4 seconds (time unit of 4 seconds ensures consistency
with the time units for the binding lifetime). A value of 0
indicates that the MAG will send an updated ANI mobility option as
soon as it discovers a change in ANI values. A non-zero value
indicates that the MAG may not send ANI values immediately after
they have changed but rather send ANI updates when the
Update-Timer expires.
4. Protocol Considerations
The following considerations apply to the LMA and the MAG.
4.1. MAG Considerations
o The conceptual Binding Update List entry data structure maintained
by the mobile access gateway, described in Section 6.1 of
[RFC5213], is extended to store the access-network-related
information elements associated with the current session.
Specifically, the following parameters are defined:
* civic location
* MAG group identifier
* ANI Update-Timer
o If the mobile access gateway is configured to support the Access
Network Information sub-options defined in this specification, it
includes this option with the specific sub-options in all PBU
messages (including PBUs for lifetime extension and for
deregistration) that it sends to the LMA. The Access Network
Information option is constructed as specified in Section 3.
o ANI Update-Timer Considerations: The MAG sets the Update-Timer
based on an exchange of timer values with the LMA. When the ANI
Update-Timer sub-option is carried in a PBU, it is considered as a
proposed value for the Update-Timer. The LMA may change the value
of the Update-Timer received in the PBU. When the LMA-provided
value for the Update-Timer is different than what is sent by the
MAG, the MAG should use the LMA-provided value. If the MAG does
not receive an ANI Update-Timer sub-option in the Proxy Binding
Acknowledgement (PBA) (in response to sending the sub-option in

the PBU), then MAG behavior is in accordance to [RFC6757]. When
ANI parameters of a mobility session change, the MAG checks
whether the Update-Timer has expired. If the Update-Timer has
expired, the MAG sends a PBU with the ANI option. The ANI option
reflects the updated access network parameters for that mobility
session. If the Update-Timer has not expired, the MAG does not
send a PBU. When the Update-Timer for a mobility session expires,
the MAG checks whether the ANI parameters have changed. If the
parameters have changed from the last reported values, the MAG
sends a PBU with an ANI option. If the parameters have not
changed, the MAG does not send a PBU (and the Update-Timer remains
expired). Note that the MAG may send a PBU even before the
Update-Timer expires. This could be, for example, to initiate a
QoS service request to the LMA (see [RFC7222]). In such cases,
the MAG must reset the Update-Timer when it sends a PBU.
o If the mobile access gateway had any of the Access Network
Information mobility options included in the PBU sent to an LMA,
then the PBA received from the LMA should contain the Access
Network Information mobility option with the specific sub-options.
If the mobile access gateway receives a PBA with a successful
Status Value but without an Access Network Information mobility
option, then the mobile access gateway may log the event and,
based on its local policy, even proceed to terminate the mobility
session. In this case, the mobile access gateway knows the LMA
does not understand the Access Network Information mobility
option.
4.2. LMA Considerations
o The conceptual Binding Cache entry data structure maintained by
the LMA, described in Section 5.1 of [RFC5213], is extended to
store the access-network-related information elements associated
with the current session. Specifically, the following parameters
are defined:
* civic location
* MAG group identifier
* ANI Update-Timer
o On receiving a PBU message from a MAG with the ANI option, the LMA
must process the option and update the corresponding fields in the
Binding Cache entry. If the option is not understood by that LMA
implementation, it will skip the option and process the PBU
without these options.

o If the received PBU message does not include the Access Network
Information option, then the mobility session associated with that
PBU is updated to remove any access network information elements.
o If the LMA understands/supports the Access Network Identifier
mobility sub-options defined in this specification, then the LMA
echoes the Access Network Identifier mobility option with the
specific sub-option(s) that it accepted back to the mobile access
gateway in a PBA. The Civic-Location and MAG-Group-Identifier
sub-options defined in this specification should not be altered by
the LMA. The LMA may change the value of the ANI Update-Timer
sub-option. It may choose to either echo the same value or
increase or decrease the timer value. For example, if the LMA
does not want to receive frequent updates (as implied by the timer
value), it may choose to increase the value. Similarly, if the
LMA needs to receive ANI updates as soon as possible, then it may
set the value to zero (0) in the PBA.
5. IANA Considerations
IANA has registered the values described below.
o This specification defines a new Access Network Identifier sub-
option called the Civic-Location sub-option. This mobility sub-
option is described in Section 3.1 and this sub-option can be
carried in the Access Network Identifier mobility option. The
type value <4> has been allocated from the registry "Access
Network Information (ANI) Sub-Option Type Values".
o This specification defines a new Access Network Identifier sub-
option called the MAG-Group-Identifier sub-option. This mobility
sub-option is described in Section 3.2 and this sub-option can be
carried in Access Network Identifier mobility option. The type
value <5> has been allocated from the registry "Access Network
Information (ANI) Sub-Option Type Values".
o This specification defines a new Access Network Identifier sub-
option called the ANI Update-Timer sub-option. This sub-option is
described in Section 3.3 and this sub-option can be carried in the
Access Network Identifier mobility option. The type value <6> has
been allocated from the registry "Access Network Information (ANI)
Sub-Option Type Values".

6. Security Considerations
The Civic-Location sub-option defined in this specification is
carried in the Access Network Identifier option defined in [RFC6757].
This sub-option is carried in PBU and PBA messages. This sub-option
is carried like any other Access Network Identifier sub-option as
defined in [RFC6757]. Therefore, it inherits its security guidelines
from [RFC5213] and [RFC6757] and does not require any additional
security considerations.
The Civic-Location sub-option exposes the civic location of the
network to which the mobile node is attached. This information is
considered to be very sensitive, so care must be taken to secure the
Proxy Mobile IPv6 signaling messages when carrying this sub-option.
The base Proxy Mobile IPv6 specification [RFC5213] specifies the use
of IPsec for securing the signaling messages, and those mechanisms
can be enabled for protecting this information. Operators can
potentially apply IPsec Encapsulating Security Payload (ESP) with
confidentiality and integrity protection for protecting the location
information. The other way to protect the sensitive location
information of network users is of course to not send it in the first
place. Users of the Civic-Location sub-option should provision
location values with the highest possible level of granularity, e.g.,
to the province or city level rather than provisioning specific
addresses.
Access-network-specific information elements that the mobile access
gateway sends may have been dynamically learned over DHCP or using
other protocols. If proper security mechanisms are not in place, the
exchanged information between the MAG and LMA may be compromised.
This situation may result in incorrect service policy enforcement at
the LMA and impact other services that depend on this access network
information. This threat can be mitigated by ensuring the
communication path between the mobile access gateway and the access
points is properly secured by the use of IPsec, Transport Layer
Security (TLS), or other security protocols.